Limit switch control for a motor drive



Feb. 28, 1967 D. R. JACOBS 3,306,997

LIMIT SWITCH CONTRL FOR A MOTOR DRIVE Filed May 6, 1965 @Mik/1 9W UnitedStates Patent O 3,306,997 LIMIT SWITCH CNTROL FOR A MUTOR DRIVE David R.Jacobs, Bluffton, Ind., assigner to Franklin Electric Co., Inc.,Bluffton, Ind., a corporation of Indiana Filed May 6, 1965, Ser. No.453,587 12 Claims. (Cl. 20D-47) This invention relates to motor driveunits, and more particularly to a limit switch control for a motor driveunit.

A motor drive unit of the type designed to be connected to move a memberbetween two positions, such as a motor drive unit for raising andlowering a garage door, requires limit switches which are responsive tothe arrival of the member at the `two limits of movement of the memberto turn off the motor drive unit. In a garage door opener, for example,the limit switches are connected to turn ofi the drive unit both whenthe door is all the way up and is all the way down.

It is a principal object of this invention to provide a limit switchcontrol for a motor drive unit, which may be easily and accuratelyadjusted to turn off the motor drive unit at precisely the desiredpositions of the member being driven.

lt is another object of the invention to provide a limit switch controlof the foregoing character, which will not easily fall out ofadjustment.

Other objects and advantages of the invention will become apparent fromthe following description taken in conjunction with the accompanyingfigures of the drawing, in which:

FIG. l is a perspective view of a motor drive unit including a limitswitch control constructed in accordance with the invention;

FIG. 2 is an enlarged view showing the limit switch control;

FIG. 3 is an exploded perspective view of the limit switch control;

FIG. 4 is a view showing a portion of the limit switch control;

FIG. 5 is a view similar to FIG. 4 but showing the portion of the limitswitch control during adjustment; and

FIG. 6 is an enlarged fragmentary sectional view taken on the line 6 6of FIG. 2.

Briey, a limit switch control embodying the invention is designed tocontrol the extent of rotation in both directions of a motor drive unithaving a rotating power output shaft. The limit switch control includesa cam drive shaft connected to the power output shaft for rotationtherewith7 and a limit shaft rotatably mounted adjacent the cam driveshaft. Two cam members are positioned on the limit shaft, one of the cammembers being secured to the limit shaft for rotation therewith and theother of the cam members being loose on the limit shaft. The latter cammember is connected by a gear arrangement to be rotated by the cam driveshaft. The two cam members are connected together by a clutcharrangement including a plurality of radially extending teeth onengageable surfaces of the two cam members, and the two cam members arespring urged toward each other. When the two cam members are clutchedtogether, rotation of the cam drive shaft produces rotation of the twocam members and the limit shaft, and the construction is such thatnumerous revolutions of the cam drive shaft are required to cause onerevolution of the limit shaft.

The limit switch control further includes a pair of limit switches, oneof the limit switches being connected to turn ofr the motor drive unitwhen the limit of rotation in one direction has been reached, and theother limit switch being connected to turn olf the motor drive unit whenthe limit of rotation in the other direction has been reached. A camsurface is formed on each of the two 3,3%,997 Patented Feb. 2S, 1967 cammembers, and the limit switches are positioned to be actuated lby thecam surfaces upon rotation of the cam drive shaft.

To adjust the number of revolutions of the cam drive shaft, in onedirection required to turn olf the motor, which corresponds to theposition of the driven member at which the motor drive unit will beturned oli', one of the two cam members may be adjusted relative to theother of the cam members. This is accomplished by applying a rotativeforce on the limit shaft. The cam member which is connected to the camdrive shaft through the gear connection, and is loose on the limitshaft, will remain angularly stationary while the other of the cammembers, which is secured to the limit shaft, will turn with the limitshaft. The ridges formed by the teeth of the clutch connection urge thetwo cam members slightly apart against the action of the spring and aclick may be heard as the teeth of the clutch pass each other and snapback together. The number of teeth of the clutch is preferably relatedto a one-to-one ratio to the gear ratio between the cam drive shaft andthe limit shaft, and therefore one click of the clutch teeth representsone revolution of the power output drive shaft. Consequently, the extentof rotation of the powerv output shaft may easily ybe adjusted by rstnoting the increase or decrease in the number of revolutions of thepower output shaft desired, and then turning the limit shaft until acorresponding number of clicks are heard.

Since a large number of radially extending teeth may be provided in theclutch, a very large number of possible angular positions of one cammember relative to the other cam member may be obtained, and the limitshaft is made easily accessible for adjustment. Further,

vimproved results are obtained by the loose mounting on the limit shaftof the cam member which is engaged by the cam drive shaft, while theother of the cam members is rigidly secured to the shaft, becauserotation of the cam drive shaft and the motor unit is not necessary whenmaking an adjustment.

In greater detail, in FIG. l is shown a motor, indicated -by the numeral1l), having a rotor shaft (not shown). The rotor shaft is connectedthrough a gear box 11 to a cam drive shaft 12, which may be an extensionof the power output shaft of the motor-gear box unit or a shaftconnected to be rotated by the power output shaft. Fastened to the sideof the gear box 11 is a limit switch control 14 which is fastened to thegear box 11 as by a plurality of bolts 16.

With reference to FIG. 2, the limit switch control 14 comprises ahousing 17 having a plurality of holes 18 formed therethrough for thebolts 16. A cover 19 for the housing is also provided, the bolts 16extending through holes formed in the cover and securing the cover 19 tothe housing as well as securing the housing to the box 11. Mountedwithin the housing 17 are two electric limit switches 21 and 22 havingterminals 23 and 24, respectively. Conductors 25 are secured to theterminals for making electrical connction with an external power circuit(not shown). The conductors 25 extending through a hole 20 in thehousing 17. The limit switch control 14 also further includes a limitshaft 26 which is journaled at its ends in two holes 27 and 28 (FIGS. 2and 6) formed in the housing 17. With reference to FIG. 3, acircumferential groove 29 is formed in the shaft at the hole 28, and apin 31 is secured to the housing and extends into the groove 29 toprevent substantial axial movement of the limit shaft 26 in the housing17.

Mounted on the limit shaft 26 are an adjustable face cam member 33 and alfixed face cam member 34, the former cam member 33 being secured to thelimit shaft 26, as by knurling a portion 30 of the surface of the shaftf buttons 53 and 54 opens the 26 and pressing the member 33 on theknurled portion, and the latter cam member 34 being loosely mounted onthe limit shaft 26. A compression spring 36 is positioned around thelimit shaft 26 between the cam member 34 and a snap ring 35, and urgesthe fixed cam member 34 toward the adjustable cam member 33. The snapring 35 is positioned around the shaft 26 in a groove 35a formed in theshaft 26, and a washer 35h is positioned between the other end of thespring 36 and the cam member 34. When the terms xed and adjustable areused herein with regard to the two cam members 33 and 34, it is meantthat the cam member 33 is adjustable in the rotary direction with theshaft 26 but is substantially stationary in the axial direction, whilethe cam member34 is axially movable relative to the shaft 26.

One end of the cam drive shaft 12 extends into the limit switch controlhousing 17 adjacent the cam member 34, and this end of the shaft 12 hasa worm 37 formed on it. The cam member 34 is cylindrical and its outersurface has axially extending gear teeth 38 formed on it, which meshwith the worm 37 of the shaft 12. Therefore, rotation of the cam driveshaft 12 also causes rotary movement of the cam member 34.

The two cam members 33 and 34 are adjustably connected together by aclutch arrangement including similar sets of V-shaped radially extendingclutch teeth 41 and 42 formed on the cam members 33 and 34,respectively. The members 33 and 34 may, for-example, be molded plasticmembers. The cam member 34 is shown as having an annular llange 43 (FIG.4) at its outer periphery, the flange 43 extending around an annularaxially extending ange 44 formed on the cam member 33. The adjacentsurfaces of the flanges 43 and 44 act as a guide during movement of thecam member 34 relative to the cam member 33. The clutch teeth 41 and 42are formed on the outer -radially extending surface of the flange 44 andon an adjacent radially extending surface of the cam member 34. Themembers 33 and 34 are also provided with hubs 46 and 47, respectively,which engage the shaft 26, and the interior of the members 33 and 34 maybe recessed between the surfaces having the teeth 41 and 42, and thehubs 46 and 47.

The spring 36 urges the cam members together and tends to hold the teeth41 and 42 in engagement. When the teeth 41 and 42 are engaged as shownin FIGS. 2 and 4, rotation of the cam drive shaft 12 causes rotation ofthe cam member 34 due to the connection between the worm 37 and gearteeth 38, and the clutch connection, including the sets of teeth 41 and42, imparts motion from the cam member 34 to the cam member 33 and thelimit shaft 26.

The two cam members 33 and 34 are respectively provided with raised camsurfaces 51 and 52 on their radial sides which are away from the teeth41 and 42. The limit switches 21 and 22 are provided with depressibleactuating buttons 53 and 54, respectively, and the limit switches 21 and22 are positioned such that the cam surfaces 52 and 51 are engageablewith the two buttons 53 and S4. Upon rotation of the limit shaft 26 andthe two cam members 33 and 34 in one direction, the cam surface 52engages the button 53 and actuates the limit switch 21, and uponrotation of the limit shaft 26 in the opposite direction, the camsurface 51 engages the button 54 and actuates the other switch 22, Thedrive motor 10 is connected in a conventional manner to be energizedthrough the switches 21 and 22, and depression of the switches 21 and22. Therefore, if the drive motor is energized for rotation in onedirection, energization will continue until the cam member 52 engagesthe button 53 and actuates the limit switch 21 to turn off the motor.Energization of the motor 10 in the opposite direction rotates the limitshaft 26 and the two cam members in the opposite direction until theraised cam surface 51 engages the button 54 of the other limit switch 22and again deenergizes the motor 10. v

It will be apparent that the number of revolutions of the motor 10required to go from one limit to the other, depends upon the gear ratiobetween the worm 37 and the gear 38 teeth.

The construction of the teeth 41 and 42 of the clutch, and theconstruction of the worm 37 and gear 38 teeth are preferably such thatthe angular separation between adjacent teeth of each set of teeth 41and 42, is equal to the angular displacement of the two cam members 33and 34 due to one complete revolution drive shaft 12. Therefore, whenadjusting the position of Ithe cam member 33 relative to the cam member34, the number of revolutions of the drive shaft 12 to be increased ordecreased is determined and the two cam members 33 and 34 are thenangularly displaced a corresponding number of clutch teeth 41 and 42.

To aid in ease of adjustment of one of the cam members relative to theother of the cam members, the ends of the limit shaft 26 are providedwith slots 56 which may be engaged by a screw driver from outside lthehousing 17 of the limit switch control. As previously stated, holes 27and 2S are formed in the housing 17, and the ends of the shaft 26 aremounted in the holes 27 and 28 with the slots 56 appearing at the outerends of the holes so that the slots 56 may be engaged by a screwdriverexternally of the housing 17.

To explain the operation of the unit, assume that the unit has its poweroutput shaft connected to raise or lower a garage door, for example. Thepower output shaft may ybe connected to the door such that the switch 22is actuated by the cam S1 when the garage door reaches the upperposition. To adjust the lower position of the garage door at which themotor 10 will be deenergized, the llrst step may be to determine thedistance of travel of the garage door caused by one revolution of thedrive shaft 12. Then, the total number of revolutions of the shaft 12 toprovide the desired adjustment may be determined. If it is decided, forexample, that an adjustment equalling three revolutions of the shaft 12is required, a screw driver is inserted into one of the slots 56 androtary force is applied to turn the shaft 26 in one direction or theother, depending upon whether it is desired to increase or decrease theheight of the garage door at which the motor 10 is to be turned off.Since the shaft 26 and the cam member 33 are axially stationary, exceptfor slight movement due to play between the pin 31 and the sides of thegroove 29, and the cam member 34 is held against substantial rotationdue to the engagement of the gear teeth 38 with the worm 37, the rotaryforce applied to the shaft 26 causes the cam member 34 to move axiallyaway from the other cam member 33 as the teeth 41 and 42 pass eachother. The fact that the gear teeth 38 extend axially and that the outersurfaces of the member 34, having the teeth 38 formed thereon is flat,enables the member 34 to move axially without interference due to theengagement of the teeth 38 with the worm 37. FIG. 5 shows the two cammem-bers separated by an amount which is substantially more than wouldoccur during operation, and is intended to further illustrate theconstruction of the cam members. The ridges formed by the teeth 41 and42 urge the two cam members 33 and 34 apart against the action of thespring 36, and a click will usually be heard as the teeth pass eachother and reengage. Furthermore, since the angular distance between theteeth 41 and 42 is related in a one-to-one ratio with the gear ratiobetween the worm 37 and the gear teeth 38, rotation of the shaft 26sutlcient to cause 3 clicks will result in an adjustment equivalent tothree complete revolutions of the shaft 12. Even if a click cannot beheard, the action of the teeth passing each other may be felt throughthe screw driver. As soon .as the rotative force applied to the limitshaft 26 is removed, the teeth 41 and 42 will be held in mutualengagement by the force of the spring 36.

The limit switch control described has numerous advantages. For example,the relative positions of the two cam members 33 and 34 may be easilyadjusted from outside the housing 17 of the control unit, making itunnecessary to remove the cover 19 in order to make an adjustment.Furthermore, an adjustment may be made either with or without powerapplied to the motor Still further, an accurate adjustment may Ibe madebecause of the relationship between the teeth 41 and 42, and the gearratio between the worm 37 and the gear teeth 38, which produces oneclick for each revolution of the cam drive shaft 12. Still another.advantage of the construction is that a setting of the limit switchcontrol is positive and relatively permanent. In other words, it is noteasily changed by accident. Also, the limit switch setting will not bechanged by vibration of the unit, by manual turning of the power outputshaft of the motor unit, or through a careless adjustment of the unit.

I claim:

1. A limit switch control for a motor drive unit, comprising a rotatablymounted limit shaft, a pair of cam members on said limit shaft, a pairof limit switches positioned adjacent said members and adapted to beactuated by the respective cam members on rotation of the latter, one ofsaid cam members being secured to said limit shaft for rotationtherewith, one of said cam members including a worm wheel, a worm fordriving said worm wheel, said cam members having adjacent end facesprovided with interengaging teeth, and spring means tending to move oneof said cam members axially toward the other to effect engagement ofsaid teeth, said limit shaft having means on at least one end thereoffor engagement by a tool for rotating said limit shaft, said teeth beingformed to cam said cam members apart on rotation of said limit shaft bysaid tool and said spring means causing said teeth to produce an audibleclick when the teeth on the respective cam members pass each other, thenumber of teeth on said cam members having a predetermined relation tothe rotation of said worm, whereby the number of clicks indicates theamount of adjustment of said worm.

2. Apparatus as in claim 1, wherein said one cam member which includes aworm wheel is axially and rotatably movable on said limit shaft, andsaid spring means comprises a compression spring which is positionedaround said limit shaft, one end of said spring being axially stationaryrelative to said shaft and the other end of said spring operablyengaging said cam member which includes said worm wheel.

3. Apparatus as in claim 1, and further including a housing for saidcontrol, said limit shaft being rotatably mounted in said housing, saidhousing having an opening formed therein, and said end of said limitshaft which is engageable by a tool being accessible through saidopening, whereby said adjustment may be made without the necessity ofopening up said housing.

4. Apparatus as in claim 1, wherein said one cam member including a wormwheel is moved axially away from the other of said cam members as saidteeth cam said cam members apart.

5. Apparatus as in claim 1, wherein said one cam member including a wormwheel is cylindrical, and the worm wheel includes axially extendingteeth formed on the outer periphery of said one cam member.

6. Apparatus as in claim 1, wherein said cam members have generallycylindrical, axially extending guide surfaces formed thereon, said guidesurfaces being mutually engageable and guiding the relative axialmovement of said cam members.

7. Apparatus as in claim 1 and further including a housing for saidlimit switch control, said housing having holes formed therein and theends of said limit shaft being rotatably positioned in said holes, andmeans for preventing substantial axial movement of said limit shaftrelative to said housing, comprising an annular groove formed in saidlimit shaft, and a pin secured to said housing and extending into saidgroove.

3. A limit switch control for a motor drive unit including :a rotatablepower output shaft, comprising a limit shaft, a pair of cam members onsaid limit shaft, a pair of limit switches positioned adjacent said cammembers and adapted to be actuated by the respective cam members onrotation of the latter, one of said cam members being secured to saidlimit shaft for rotation therewith and the other of said cam membersbeing loosely mounted on said limit shaft, means for connecting saidlimit shaft to said power output shaft for rotation thereby, said cammembers having adjacent faces provided with interengaging clutch teeth,and biasing means tending to move said cam members toward each other toeffect engagement of said teeth, said limit shaft having means on atleast one end thereof for engagement by a tool for rotating said limitshaft, said connecting means being operable to hold the cam member whichis loose on the limit shaft against rotation when said limit shaft isrotated by said tool, said teeth being formed to cam said cam membersapart on rotation of said limit shaft by said tool, and said biasingmeans causing said teeth to produce an audible click when said teeth onthe respective cam members pass each other, the number of teeth on saidcam members having a predetermined relation to the rotation of the poweroutput shaft, whereby the number of clicks indicates the adjustment ofthe point at which the limit switch associated with the cam membersecured to said limit shaft will be actuated.

9. A limit switch control for a motor drive unit including a rotatablepower output shaft, comprising a pair of cam members, a pair of limitswitch members, each of said switch members being associated with one ofsaid cam members, means for rotatably mounting one of said pairsrelative to the other of said pairs, said limit switch members beinglocated adjacent the cam members and being actuated by the respectivecam members on relative rotation of said one pair, means adapted toconnect one of said members of said one pair to the power output shaftfor rotation of said one member in timed relation with said power outputshaft, said members of said one pair being rotatably and axially movablerelative to each other, and clutch means for connecting said members ofsaid one pair, said clutch means including a set of clutch teeth on eachof said members of said one pair, said teeth extending substantiallyradially of the axis of rotation of said one pair, and means for biasingsaid members toward each other to move said sets of teeth intoengagement, said connecting means comprising a worm and gearconstruction, said worm being rotatable on rotation of said power outputshaft and said gear being rigid with said one member of said one pair,and the angular separation of said clutch teeth being substantiallyequal to the angular distance said gear travels due to one completerevolution of said worm.

10. Apparatus as in claim 9, wherein said rotatably mounted paircomprises said pair of cam members.

11. Apparatus as in claim 9, wherein said means for rotatably mountingone of said pairs comprises a limit shaft, and means for rotatablymounting said limit shaft, one of said members of said one pair beingsecured to said limit shaft and the other of said members of said onepair being loosely mounted on said limit shaft.

12. A limit switch control for a motor drive unit including a rotatablepower output shaft, comprising a pair of cam members, a pair of limitswitch members, each of said switch members being associated with one ofsaid cam members, means for rotatably mounting one of said pairsrelative to the other of said pairs, said limit switch members beingactuated by the respective cam members on relative rotation of said onepair, means adapted to connect one of said members of said one pair tothe power output shaft for rotation of said one member in timed relationwith said power output shaft, said members of said one pair -beingrotatably and axially movable relative to each other, and clutch meansfor connecting said members of said one pair, said clutch meansincluding a set of clutch teeth on each of said members of said onepair, said teeth extending substantially radially of the axis ofrotation of said one pair, means for biasing said members toward eachother to move said sets of teeth into engagement, said means forrotatably mounting one of said pairs comprising a limit shaft, and meansfor rotatably mounting said limit shaft, one of said members of said onepair being secured to said limit shaft and the other of said members ofsaid one pair being loosely mounted on said limit shaft, a housing forsaid members and said limit shaft, a cover for said housing, and atleast one end of said limit shaft having means formed thereon forengagement by a tool. said limit shaft being mounted in said housingwith said one end accessible from outside said housing, whereby anadjustment may be made without the necessity of removing said cover.

References Cited by the Examiner UNITED STATES PATENTS 2,468,974 5/1949Hammer 200--153 X 2,711,450 6/1955 Carr 20G-153 X 2,876,313 3/1959 Dullet al. ZOO-153 3,l75,4l8 3/1965 Schaefer ZOO-47 X BERNARD A. GILHEANY,Primary Examiner.

T. MACBLAIN, Assistant Examiner.

1. A LIMIT SWITCH CONTROL FOR A MOTOR DRIVE UNIT, COMPRISING A ROTATABLYMOUNTED LIMIT SHAFT, A PAIR OF CAM MEMBERS ON SAID LIMIT SHAFT, A PAIROF LIMIT SWITCHES POSITIONED ADJACENT SAID MEMBERS AND ADAPTED TO BEACTUATED BY THE RESPECTIVE CAM MEMBERS ON ROTATION OF THE LATTER, ONE OFSAID CAM MEMBERS BEING SECURED TO SAID LIMIT SHAFT FOR ROTATIONTHEREWITH, ONE OF SAID CAM MEMBERS INCLUDING A WORM WHEEL, A WORM FORDRIVING SAID WORM WHEEL, SAID CAM MEMBERS HAVING ADJACENT END FACESPROVIDED WITH INTERENGAGING TEETH, AND SPRING MEANS TENDING TO MOVE ONEOF SAID CAM MEMBERS AXIALLY TOWARD THE OTHER TO EFFECT ENGAGEMENT OFSAID TEETH, SAID